What happened
On August 12, 2017, a Schleicher ASK 21 glider, registration I-NIBO, departed from Calcinate del Pesce aerodrome in Italy for a local flight. The flight was operated by two pilots with relatively limited flight experience. After nearly two hours of soaring, the crew realized that due to a lack of rising air, they could no longer return to their departure airfield. At this point, the aircraft had already drifted outside the safe landing cone of the home aerodrome.
Seeking an alternative, the pilots identified a field approximately 1.2 km southwest of Stabio, Switzerland, as a suitable landing site. While attempting to manage their descent, the crew performed several spiral turns, losing altitude continuously. During the final approach, the pilot initiated a single, continuous 270-degree right turn at an altitude of only 95 meters above the ground. The approach was flown at an indicated airspeed of 110 km/h with a steep descent angle and fully extended airbrakes. The glider struck the ground heavily about 90 meters before the end of the field, resulting in one injury (a spinal fracture to the rear occupant) and severe damage to the aircraft's forward fuselage and nose gear.
The investigation
SISI examined flight data from the aircraft's Flarm device and statements from both pilots. The investigation focused on the flight path, the decision-making process regarding the landing site, and the execution of the final approach. The investigation confirmed that the aircraft was in good technical condition and that the pilots were properly licensed for the flight.
Findings
- The primary cause of the accident was the inappropriate distribution of the landing pattern, specifically the use of a single continuous turn rather than a standard approach consisting of base and final legs.
- An error in altitude estimation likely led to the pilot initiating the turn much too low.
- The steep descent angle and high approach speed were necessitated by the need to avoid a fence at the edge of the field.
- An additional contributing factor was the crew's unawareness that they had flown outside the safety cone of the departure aerodrome, which left them without sufficient altitude reserves for a return to base.